Cutting inserts are used in various cutting tools for the machining of workpieces, particularly metallic workpieces. Indexable cutting inserts, formed from material such as sintered carbides or ceramics, are often used in milling operations, such as machining aluminum, cast iron, steel, stainless steel, nickel based alloys, cobalt alloys, and titanium. Examples of cutting tools that employ inserts in performing milling operations include face mills, end mills and slotters.
In some conventional cutting tools, indexable cutting inserts are removably secured in insert seats disposed within pockets and spaced circumferentially around the outer periphery of a tool body. Conventional inserts may have a cutting edge about the outside of the insert, which provides a number of alternately usable cutting edges. In some cutting tools, a polygonal insert has been employed to make effective use of its corners.
Ordinarily, during a cutting operation, only a portion of the cutting edge actually cuts the workpiece. When one cutting position becomes worn, the insert may be “indexed,” or repositioned, in the seat in order to bring a fresh cutting edge into the active cutting position. When all of the cutting positions are worn, the insert is discarded and replaced with a new one. In such conventional cutting tools, inserts are generally indexed by rotating them in their respective insert seats about an axis defined by the retainer hole to expose a different cutting edge.
The tool body of a conventional cutting tool often has a circular working end and a plurality of pockets, and chip gullets, positioned about the outside circumference of the working end, and each station contains a seating surface for mounting a cutting insert. An insert seat ordinarily includes one or more seating surfaces for locating, positioning, and orienting the insert in the pocket. One of many methods of retention is a common screw, which passes through a retainer hole in each insert and is threaded into a threaded mounting hole in a seating surface to retain the insert in the pocket. Each chip pocket forms a recess, or indentation, in the tool body located between adjacent insert seats. The chip pockets provide clearance regions for chips cut during the operation of the cutting tool.
A conventional threaded hole is generally perpendicular or slightly angled to the broad top and bottom faces of the insert and to the seating surface supporting the bottom face. During cutting of the workpiece, the inserts commonly experience forces that act to tend to cause the insert to be ejected from the insert pocket. The retainer fastener is the primary means by which the insert is retained in the seat. As a result, the retainer is subject to a shear force that can result in the breaking of the retainer.
In addition, the orientation of the retainer in the insert seat requires the removal of a significant amount of the cutting tool body in front of the insert seat. More specifically, the retainer is oriented approximately perpendicular to the face of the major seating surface, i.e., the seating surface in contact with the bottom face of the insert. As a result, a significant amount of the cutting tool body in front of each major seating surface must be removed to allow the retainer to be screwed in and out of the major seating surface. The removal of this cutting tool body material makes the cross-section smaller, thereby weakening it and shortening its useful life.
Thus, there is a need for an improved cutting insert and an improved cutting tool body. There is a need for a cutting insert having a geometry that decreases the shear force on the retainer and that allows the insert to be mounted in the insert seat more securely. Also, there is a need for a cutting tool body having a cooperating geometry that decreases the shear force on the retainer and that holds the inserts in the pockets more securely. Further, there is a need for a stronger, thicker cross-section cutting tool body allowing smaller chip pockets, if desired, improved cutting ability, increased strength, and a longer useful life.